Only mineral deposits with sufficient metalliferous content can be economically mined and processed to produce the metallic constituents. Marginal ores, old tailings, or even good ores, can be enriched to provide a more desirable raw material for the smelting or refining processes. Flotation processes, both liquid and air, have long been used to separate at least a large part of the gangue from the virgin ore to effect the desired enrichment of the ore for further processing. The general object of this invention is to provide improved air flotation apparatus for enriching ore which is, or has been reduced to, small particles similar in size, roughly, to natural sands.
Apparatus of this type is described in Hoffman U.S. Pat. No. 2,798,607. This apparatus has proved to be without commercial utility, however, partly because of impedance of the flow of the flotation suspension by blades intended to laterally divert and discharge the floating gangue, this interference tending to clog the stream and prevent operation of the apparatus. Excessive care also had to be taken to prevent choking of the apparatus at the inlet end by the ore being fed from a hopper. Also, even when subjected to vibration, the herringbone pattern of riffle grooves does not dependably carry away separated valuable ore. Although Hoffman provides means for separately controlling the flow of air to the feed section, the intermediate deck, and the discharge section of his separation trough, respectively, he apparently contemplates the maintenance of equal air pressures under each section in the operation of his apparatus or, at most,to adjust air to compensate for the changing load of solids carried in the flotation stream.
It must be recognized that to be successful the air flotation process that is carried out with a particular apparatus must be adapted to the pertinent characteristics of the ore to be processed as it is fed to the apparatus. Since the flotation characteristics of the particles fed to the apparatus depends upon the densities of the particles and their dimensions and shapes, the enriching apparatus must be adapted to the flotation conditions required to separate gangue from the valuable ore in each raw material mixture. Most important, the upward air flow through the classification trough floor must be sufficient to effect the essential suspension of at least the gangue particles. In the apparatus of the instant invention, this is accomplished in two stages, the first being the immediate air impregnation and suspension of the mass of mixed particles as fed to the inlet section of the trough from a hopper, the second stage providing maintenance of the suspension so that the fluidized body flows through the trough to its discharge end as the less buoyant valuable ore settles in the riffles of the floor plates and the floating gangue is separated and discharged. The enrichment of the ores by separation of the gangue from the value particles is comparatively easy and efficient when operating upon a mixture in which a comparatively large differential exists between the "buoyancy" of the gangue particles and of the value particles. A more exacting control of the rate of upward flow of the flotation air is required to separate particles which have comparatively similar flotation or buoyancy characteristics.
The object of the present invention is to provide air flotation apparatus for enrichment of ore in particle form by separation of at least a substantial part of the gangue, the apparatus embodying air flow control means for supplying flotation air in relatively very copious quantities to the inlet section of the separation trough to effect immediate impregnation without time lag and flotation of the ore particles as the raw material is supplied to the apparatus while providing a relatively greatly reduced flow of flotation air to the classification section of the trough. The trough is entirely unimpeded to the flow of the fluidized body throughout the length thereof to avoid any interruption to the generally uniform and continuous flow of the suspension through the apparatus.
A further object is to provide such enrichment apparatus wherein the floor is composed of a succession of modular, adjoining air-diffusing plates providing either crosswise or lengthwise riffles to trap the value particles as may be best adapted to the processing of a particle raw material mixture. The crosswise riffle orientation is usually employed in batch operation while the lengthwise orientation, advantageously with a shaker or vibrating conveyor device, may be operated continuously.
A further object is to provide such apparatus which may be adapted to the efficient processing of ores containing heavy metal components, such as lead or gold, by forcing flow of diffused flotation air through the bottom portions of even partly filled riffle troughs by sealing over the peak areas between the riffles of the floor plates.